Apoptosis, "programmed cell death," is a cellular process exhibiting distinct biochemical and morphological changes, and is a key element of both normal and disease processes at the cellular level. As such, apoptosis is the subject of thousands of publications annually, yet none of the assays that are commonly used to detect or track apoptosis are performed on viable cells, as all require disruption of cultures or tissue, often by fixation and staining. A nondisruptive assay of apoptosis would enable real-time monitoring of cells and cell cultures, dramatically facilitating such studies, and generally eliminating standard labor-intensive assays. Additional impact would obtain if the method could expose and identify specific apoptotic pathways. Moreover, since massive apoptosis is one of the earliest indications of response to most types of anti-cancer treatment, a longer-term (after this project) in-vivo application of a noninvasive assay could impact management of cancer treatment. Elastic scattering spectroscopy (ESS) is a noninvasive, real-time, optical method that uses light scattering measurements to obtain quantitative information about the micromorphology of cells and tissue. This project will develop and test novel instrumentation that uses ESS and is specifically designed to realize nondisruptive, quantitative monitoring of apoptosis in viable cell cultures in real time, for both plated cultures and cell suspensions. This will be effected by measuring the wavelength-dependence (spectrum) of scattered light at selected angles, and the angle-dependence (phase function) of scattered light at specific wavelengths, from individual cells or ensembles of cells in culture, either in suspension or in conventional culture plates. The spectral ESS system will incorporate a specialized "mini-incubator" optical chamber to maintain cells during a sequence of measurements. For measurement of the angular scattering phase function, our novel polar nephelometer will be adapted to facilitate measurements on plated cultures. Since individual measurements are nearly instantaneous, the ESS method will enable the tracking of changes in micromorphology over any desired time span. Analytical and computational methods will be used, applied to the resulting spectra and angle measurements, to extract the size distributions of scatterers within the cells, thus providing quantitative measures related to cellular ultrastructure. Extensive validations will be performed using established biochemical assays that are well understood, as well as environmental scanning electron microscopy. PUBLIC HEALTH RELEVANCE: In studying disease processes and the response of cells to treatments, it is critical to monitor and understand the mechanisms of cell death. The proposed instrumentation will enable cellular biologists, who are studying cellular response to treatment, to monitor and evaluate cell-death processes in a faster and less labor-intensive manner, by using light-based measurements instead of the current chemical assays.